1. Field of the Invention
The present invention relates to a display device, and more particularly, to a backlight unit and a liquid crystal display device having the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for an LCD backlight unit having enhanced brightness.
2. Description of the Background Art
Generally, a liquid crystal display (LCD) device is a flat panel display device. LCDs are extensively used due to the ease with which they are driven and their superior ability to display images. LCDs have been widely applied as a monitor in computers and televisions as well as an instrument display in aircrafts and ships.
An LCD device includes an LCD panel, a driving circuit unit, and a backlight unit. The driving circuit unit has integrated circuits on a printed circuit board (PCB) for driving the LCD panel. The backlight unit has a supporting structure enclosing light emitting lamps.
The backlight unit is the light source of the LCD device and consumes most of the power used by the components of the LCD device. Thus, a backlight unit emitting a bright light with a minimum amount of power is important in reducing the overall power used by the LCD device. The backlight also has to supply the same degree of brightness to each area of the LCD panel, so that the LCD device displays an image with uniform brightness.
Typically, a linear optical source, such as a fluorescent lamp, is used as the light emitting lamps in a backlight. Recently, a point optical source, such as a light emitting diode (LED), is being used to supply light to a surface of the LCD panel. Hereinafter, a related art backlight unit for an LCD device using a point optical source, such as an LED, will be explained with reference to FIGS. 1 to 3.
FIG. 1 is a cross-sectional view showing an LCD device having a backlight unit in accordance with the related art. As shown in FIG. 1, the related art LCD device has a backlight unit including an LCD panel 360 on which pixels are arranged in a matrix form and a backlight unit 300 for supplying light to the LCD panel 360. The LCD panel 360 includes a thin film transistor (TFT) array substrate (not shown), a color filter substrate (not shown) facing the TFT array substrate with a gap therebetween, and a liquid crystal layer (not shown) interposed between the color filter substrate and the TFT array substrate in the gap. Although not shown, a common electrode and a pixel electrode are respectively formed on the color filter substrate and the TFT array substrate, thereby applying an electric field across the liquid crystal layer.
The backlight unit includes a lower cover 350, a light emitting diode (LED) supporter 310 formed on an upper surface of the lower cover 350, a plurality of LEDs 330 arranged on an upper surface of the LED supporter 310 for emitting light in both horizontal and vertical directions, a light guiding plate 340 arranged above the LEDs 330 with a certain gap, a diffusion plate 347 arranged over the light guiding plate 340 for effectively diffusing light emitted from the LED 330, and a plurality of optical sheet layers 349 on the diffusion plate 347. A reflector 320 for enhancing light efficiency of the light emitted from the LED is formed below the LEDs 330.
The light guiding plate 340 is provided over all of the LEDs 330 of the backlight unit so that light emitted from the LEDs 330 can be uniformly distributed across the entire surface of the backlight unit. The LEDs can be a combination of red, green and blue LEDs. Diverters 335 for a color mixing light emitted directly from the LEDs 330 are formed on a lower surface of the light guiding plate 340 directly over each of the LEDs 330. Single-color light emitted from the LEDs 330, such as red, green or blue, is not directly displayed on the LCD panel 360 because of the diverters 335.
The LCD panel 360 and the backlight unit 300 are covered by a guide panel 351. The side surfaces of the LCD panel 360 and the backlight unit 300 are supported by a mold frame 345. An upper edge of the LCD panel 360 is fixed by a top case 370, which is coupled to the guide panel 351, and the guide panel 351 is coupled to the mold frame 345.
FIG. 2 is a cross-sectional view showing a structure of a backlight unit in accordance with the related art. As shown in FIG. 2, the related art backlight unit includes a lower cover 210, a plurality of LEDs 220 arranged on the lower cover 210 with a certain gap therebetween, a light guiding plate 230 formed above the LEDs 220 at a predetermined distance, and a plurality of diverters 235 on the light guiding plate 230 having a prism structure or formed of a reflective material corresponding to the LEDs 220. The diverter 235 prevents light from being directly emitted from the LEDs 220 and displayed on the LCD panel. The diverters aid in color mixing.
FIG. 3 is a cross-sectional view showing a direction of light emitted from a light emitting device of a backlight unit in accordance with the related art. In the related art backlight unit shown in FIGS. 1 and 2, light emitted from the LEDs is not full utilized to maximum effectiveness, which results in an inferior brightness. More specifically, as shown in FIG. 3, when power is supplied to the related art LED, approximately 20% of a total optical amount of the light is emitted in a vertical direction 12 and approximately 80% of the total optical amount is emitted in horizontal directions 14 and 16. In the related art backlight unit and the LCD device having the same, light emitted from side surfaces of the LEDs of the backlight unit is not fully utilized. Further, light emitted from the side surfaces of the LEDs of the backlight unit can be wasted due to optical absorption at the peripheral region of the backlight unit so that light is not consistently provided out to the edges of the backlight unit.